Method of reducing reperfusion injury with imidazol-2-thiones

ABSTRACT

Certain imidazol-2-thiones are reported to reduce reperfusion injury which is the injury which occurs when molecular oxygen is reintroduced into an ischemic tissue. These compounds could be used to prevent much of the damage which occurs to the heart of a heart attack victim.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 028,516, filed Mar. 20, 1987, now abandoned.

FIELD OF THE INVENTION

This invention relates to the use of certain pharmaceutical agents to reduce damage caused during reperfusion of an ischemic tissue.

BACKGROUND OF THE INVENTION

Heart attack is a leading cause of death. Until recently it was thought that the oxygen deprivation to the heart muscle, cardiac ischemia, was the significant cause of damage to the heart in heart attack victims. While true that lack of oxygen to the heart or a region of the heart will eventually result in cell death, no significant injury occurs to the heart for at least thirty to forty minutes in the absence of molecular oxygen. Recent findings suggest that the much of the injury to the heart following an ischemic event of relatively short duration occurs during the reperfusion of the ischemic tissue with oxygenated blood and may be caused by oxygen derived free radicals.

The compound 1,3-dihydro-4-methyl-5-[4-(methyl-thio)benzoyl-2H-imidazol-2-one, enoximone, and the compound 1,3-dihydro-4-ethyl-5-(4-pyridinylcarbonyl)-2H-imidazol-2-one, piroximone, are known from U.S. Pat. Nos. 4,405,635 and 4,405,628, respectively, to be cardiotonic agents useful in the treatment of heart failure, for example, congestive heart failure. Enoximone and piroximone apparently function by increasing cardiac contractility thereby increasing the pumping ability of the heart. The stronger heart is then better able to supply blood to the organs of the body. While perhaps not curing or treating the underlying condition or disease causing the heart failure, enoximone and piroximone treat the most serious symptom, i.e. lack of adequate blood supply to the tissues and organs of the body. Enoximone and piroximone may also act to relieve the symptoms of heart failure by acting as vasodilators, thereby reducing the resistance of the flow of blood to the body tissues.

1,3-dihydro-4-methyl-5-[4-(methylthio)benzoyl-2H-imidazol-2-thione, the thio analog of enoximone, and 1,3-dihydro-4-ethyl-5-(4-pyridinylcarbonyl)-2H-imidazol-2-thione, the thio analog of piroximone, the compounds of this invention, are also generically known from U.S. Pat. No. 4,405,628 and are also generically disclosed there to be cardiotonic agents. Indeed applicants have determined that the thio analog of enoximone has about one-tenth the potency of enoximone and the thio analog of piroximone about one-eighteenth the potency of piroximone in enhancing cardiac contractile stength. Now it has been discovered that the thio analog of enoximone, 1,3-dihydro-4-methyl-5-[4-(methylthio)benzoyl]-2H-imidazol-2-thione, and the thio analog of piroximone, 1,3-dihydro-4-ethyl-5-(4-pyridinylcarbonyl)-2H-imidazol-2-thione, as well as certain of their derivatives when administered to a patient prior to an ischemic event, during an ischemic event, or during the period of time subsequent to an ischemic event during which reperfusion damage occurs, prevents or lessens the damage which normally occurs when circulation is restored to the portion of the heart deprived of blood.

SUMMARY OF THE INVENTION

The imidazol-2-thiones having structure 1: ##STR1## wherein T is a divalent oxygen or sulfur group;

R₁ is a hydrogen or a (C₁ -C₄)alkyl group; and

R₂ is a phenyl group of the structure: ##STR2## wherein R₃, R₄, R₅, and R₆ are each selected from a hydrogen, (C₁ -C₄)alkyl, (C₁ -C₄)alkoxy, (C₁ -C₄)alkylthio, (C₁ -C₄)alkylsulfoxide, (C₁ -C₄)alkylsulfone, hydroxy, halogen, trifluoromethyl, --NR'R" wherein R' and R" are each selected from a hydrogen or (C₁ -C₄)alkyl group, pyrrolidino, piperidino, morpholino, piperazino, N--(C₁ -C₄)alkylpiperazino, cyano, carboxy, carboxamido, (C₁ -C₄)alkoxycarbonyl, amidino, and 1-, 2-, 3-, 4-, or 5-imidazolyl, and any two adjacent R₃, R₄, R₅, and R₆ groups can taken together form a methylenedioxy group and with the proviso that when one of R₃, R₄, R₅, or R₆ is a --NR'R", pyrrolidino, piperidino, morpholino, piperazino, or N--(C₁ -C₄)alkylpiperazino group then at least two of R₃, R₄, R₅, and R₆ must be a hydrogen group; or

R₂ is a pyridyl group optionally having one or two substitutents selected from (C₁ -C₄)alkyl, (C₁ -C₄)alkoxy, (C₁ -C₄)alkylthio, (C₁ -C₄)alkylsulfoxide, (C₁ -C₄)alkylsulfone, trifluoromethyl, cyano, carboxy, carboxamido, amidino, and 1-, 2-, 3-, 4-, or 5-imidazolyl; or R₂ is a 2- or 3-(1H)-pyrryl, 2- or 3-thienyl, or 2- or 3-furanyl;

as well as their pharmaceutically acceptable salts are useful in preventing or lessening reperfusion injury, i.e. the injury resulting from the reintroduction of molecular oxygen to an ischemic tissue.

DETAILED DESCRIPTION OF THE INVENTION

As used herein the term (C₁ -C₄)alkyl and the (C₁ -C₄)alkyl portion of the alkoxy, alkylthio, alkylsulfoxide, alkylsulfone, alkylpiperazino, and alkoxylcarbonyl groups means straight and branched chain alkyl groups having from one to four carbon atoms and includes methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl groups. The term cyano group means a group having the structure --C.tbd.N; carboxy, the structure --C(O)OH; carboxamido, the structure --C(O)NH₂ ; alkoxycarbonyl, the structure --COO(C₁ -C₄)alkyl; and amidino, the structure --C(NH)NH₂. A halogen group means a fluoro, chloro, bromo, or iodo group. A methylenedioxy group has the structure --OCH₂ O--.

The compounds of structure 1 are acidic and can form pharmaceutically acceptable salts with suitable inorganic or organic bases. These salts include those of the alkali metals such as lithium, sodium, or potassium. These salts can be prepared using conventional means such as by neutralizing a solution of the free acid in a polar solvent with a stoichiometric quantity of base, for example, an alkoxide such as sodium methoxide or potassium ethoxide or a hydride such as lithium hydride. These reactions are preferably carried out in solution. Suitable solvents are, for example, lower alcohols such as methanol, ethanol, isopropanol, or n-propanol; the ketonic solvents such as acetone or methyl ketone; or dimethylformamide (DMF). Typically about 1 molar equivalent of the free acid compound of structure 1 is allowed to react with about 1 molar equivalent of the base for about 1 minute to about 24 hours, preferably about 1 hour, depending on the reactants and the temperature which can be from about -30° C. to about 78° C., preferably about 0° C. to about 25° C. The compounds of structure 1 wherein R₂ is an optionally substituted pyridyl can form pharmaceutically acceptable salts with non-toxic organic or inorganic acids. Illustrative inorganic acids which form suitable salts include hydrochloric, hydrobromic, sulfuric, and phosphoric acids and acid metal salts such as sodium monohydrogen orthophosphate and potassium hydrogen sulfate. Illustrative organic acids which form suitable salts include the mono, di, and tricarboxylic acids. Illustrative of such acids are, for example, acetic, glycolic, lactic, pyruvic, malonic, succinic, glutaric, fumaric, malic, tartaric, citric, ascorbic, maleic, hydroxymaleic, benzoic, hydroxybenzoic, phenylacetic, cinnamic, salicylic, and 2-phenoxybenzoic acids. Other organic acids which form suitable salts are the sulfonic acids such as methane sulfonic acid and 2-hydroxyethane sulfonic acid. Such salts can exist in either a hydrated or a substantially anhydrous form. The acid salts are prepared by standard techniques such as by dissolving the free base compound of structure 1 wherein R₂ is an optionally substituted pyridyl group in aqueous or aqueous-alcohol solvent or other suitable solvent containing the appropriate acid and isolating by evaporating the solution, or by reacting the free base in an organic solvent in which case the salt separates directly or can be obtained by concentration of the solution. In general the pharmaceutically acceptable salts are crystalline materials which are more soluble in water and various hydrophilic solvents and which in comparison to the free acid or base form generally demostrate higher melting points and an increased chemical stability.

The preferred compounds of this invention are those compounds of structure 1 wherein T is a divalent oxygen atom. More preferred are those compounds of structure 1 wherein R₂ is an optionally substituted pyridyl group or wherein R₂ is a phenyl group, particularly where the phenyl group is unsubstituted or is para substituted, i.e. where R₃, R₄, and R₆ are each a hydrogen group. Even more preferred are those compounds of structure 1 wherein R₂ is an optionally substituted 4-pyridyl group or wherein R₂ is a phenyl group wherein the R₃, R₄, and R₆ substitutents are each a hydrogen group and wherein the R₅ substitutent is a (C₁ -C₄)alkylthio group and those compounds wherein R₁ is a methyl of ethyl group. Most preferred are those compounds of structure 1 wherein R₁ is a methyl or ethyl group and wherein R₂ is a 4-pyridyl group or wherein R₂ is a 4-(methylthio)phenyl group.

Representative compounds of this invention included:

1,3-dihydro-4-isonicotinoyl-2H-imidazol-2-thione;

4-[3-(n-butylthio)isonicotinoyl]-1,3-dihydro-5-methyl-2H-imidazol-2-thione;

4-(2-bromoisonicotinoyl)-1,3-dihydro-5-ethyl-2H-imidazol-2-thione;

4-[2-(n-butyl)isonicotinoyl]-1,3-dihydro-5-isopropyl-2H-imidazol-2-thione;

1,3-dihydro-4-ethyl-5-(3-methylisonicotinoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-[2-(ethylthio)isonicotinoyl]-2H-imidazol-2-thione;

1,3-dihydro-4-ethyl-5-[3-(n-propoxy)isonicotinoyl]-2H-imidazol-2-thione;

1,3-dihydro-4-nicotinoyl-2H-imidazol-2-thione;

4-(2-chloronicotinoyl)-1,3-dihydro-5-methyl-2H-imidazol-2-thione;

4-(4-bromonicotinoyl)-1,3-dihydro-5-ethyl-2H-imidazol-2-thione;

4-(n-butyl)-1,3-dihydro-5-(5-fluoronicotinoyl)-2H-imidazol-2-thione;

4-(6-chloronicotinoyl)-1,3-dihydro-5-(n-propyl)-2H-imidazol-2-thione;

1,3-dihydro-4-ethyl-5-(2-ethylnicotinoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-[4-(isobutylthio)nicotinoyl]-5-(n-propyl)-2H-imidazol-2-thione;

1,3-dihydro-4-isobutyl-5-(5-methylnicotinoyl)-2H-imidazol-2-thione;

4-(6-ethylisonicotinoyl)-1,3-dihydro-2H-imidazol-2-thione;

1,3-dihydro-4-ethyl-5-(2-isopropoxynicotinoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-(5-ethoxynicotinoyl)-5-methyl-2H-imidazol-2-thione;

1,3-dihydro-4-(6-methoxynicotinoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-picolinoyl-2H-imidazol-2-thione;

1,3-dihydro-4-(3-chloropicolinoyl)-5-ethyl-2H-imidazol-2-thione;

4-(4-bromopicolinoyl)-1,3-dihydro-5-methyl-2H-imidazol-2-thione;

1,3-dihydro-4-(5-fluoropicolinoyl)-5-isopropyl-2H-imidazol-2-thione;

4-(6-bromopicolinoyl)-1,3-dihydro-5-methyl-2H-imidazol-2-thione;

4-[3-(n-butyl)picolinoyl]-1,3-dihydro-2H-imidazol-2-thione;

4-(n-butyl)-1,3-dihydro-5-[4-(methylthio)picolinoyl]-2H-imidazol-2-thione;

1,3-dihydro-4-ethyl-5-(5-ethylpicolinoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-(6-methylpicolinoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-(3-ethoxypicolinoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-(4-isopropoxypicolinoyl-5-ethyl-2H-imidazol-2-thione;

1,3-dihydro-4-methyl-5-(5-methoxypicolinoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-(6-ethoxypicolinoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-isobutyl-5-(2-thienoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-ethyl-5-(3-furanoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-[2-(1H-pyrroyl)]-2H-imidazol-2-thione;

1,3-dihydro-4-methyl-5-[4-methoxy(thiobenzoyl)]-2H-imidazol-2-thione;

4-[2-chloro(thiobenzoyl)]-1,3-dihydro-2H-imidazol-2-thione;

4-(2,3-diethylbenzoyl)-1,3-dihydro-5-ethyl-2H-imidazol-2-thione;

4-benzoyl-1,3-dihydro-5-methyl-2H-imidazol-2-thione;

1,3-dihydro-4-methyl-5-(2-thienoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-methyl-5-(3,4-methylenedioxybenzoyl)- [2H-imidazol-2-thione;

1,3-dihydro-4-benzoyl-2H-imidazol-2-thione;

1,3-dihydro-4-(4-methoxybenzoyl)-5-methyl-2H-imidazol-2-thione;

4-benzoyl-1,3-dihydro-5-methyl-2H-imidazol-2-thione;

1,3-dihydro-4-(3,4-dimethoxybenzoyl)-5-methyl-2H-imidazol-2-thione;

1,3-dihydro-4-(2-furanoyl)-5-methyl-2H-imidazol-2-thione;

1,3-dihydro-4-(2-thienoyl)-2H-imidazol-2-thione;

4-benzoyl-1,3-dihydro-2H-imidazol-2-thione;

1,3-dihydro-4-(2-furanoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-(methoxybenzoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-(4-fluorobenzoyl)-5-methyl-2H-imidazol-2-thione;

4-(2-chlorobenzoyl-1,3-dihydro-5-methyl-2H-imidazol-2-thione;

4-(4-chlorobenzoyl)-1,3-dihydro-5-methyl-2H-imidazol-2-thione;

1,3-dihydro-4-methyl-5-(4-piperidinobenzoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-methyl-5-(4-morpholinobenzoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-methyl-5-(4-pyrrolidinobenzoyl)-2H-imidazol-2-thione;

1,3-dihydro-4-(4-dimethylaminobenzoyl)-5-methyl-2H-imidazol-2-thione;

1,3-dihydro-4-methyl-5-[4-(4-methylpiperazino)benzoyl]-2H-imidazol-2-thione;

1,3-dihydro-4-ethyl-5-[4-(methylthio)benzoyl]-2H-imidazol-2-thione;

1,3-dihydro-4-(4-hydroxybenzoyl)-5-methyl-2H-imidazol-2-thione;

1,3-dihydro-4-methyl-5-[4-(methylthio)benzoyl]-2H-imidazol-2-thione;

The compounds of structure 1 wherein T is a divalent oxygen atom are readily prepared by, for example, the procedure set forth in U.S. Pat. No. 4,405,628. Essentially this procedure requires that the aminodiketone of structure 2: ##STR3## wherein R₁ and R₂ are as defined for structure 1, be allowed to react with a thiocyanate salt, preferably sodium or potassium thiocyanate. The reaction is acid catalyzed and the additional presence of a mild acid, for example, a dilute mineral acid such as dilute hydrochloric acid sulfuric acid or phosphoric acid, a carboxylic acid such as acetic acid, trifluoroacetic acid, benzoic acid, or formic acid, or a sulfonic acid such as methanesulfonic acid or p-toluenesulfonic acid in the reaction mixture is preferred. Preferably the solvent will act as the acid catalyst. This reaction is performed by mixing about 1 molar equivalent of the aminodiketone with about 1 to about 5 molar equivalents, preferably about 2 or 3 molar equivalents of the thiocyanate salt in a suitable solvent. The reaction is allowed to proceed for about 5 minutes to about 10 hours depending on, for example, the solvent and the temperature which can be from about 0° C. to about 100° C. Conveniently the reaction can be carried out at room temperature, i.e. about 25° C., and this is preferred. Suitable solvents for this reaction can be any non-reactive solvent such as water or a water miscible solvent, for example, an organic acid such as acetic acid; an alcohol such as methanol or ethanol; or an ether such as tetrahydrofuran or p-dioxan. Preferably any non-aqueous solvent will be mixed with water. The preferred solvent is water.

The product of this reaction can be isolated and purified by any suitable art known procedures such as by evaporation of the reaction solvent. The product can be successfully purified by recrystallization from a mixture of ethanol and methanol. Conveniently when the solvent is a mixture of acetic acid and water and potassium thiocyanate is the thiocyanate salt, the product separates from the reaction mixture as a crystalline substance which can then readily be isolated by filtration.

The aminodiketone of structure 2 can be prepared by, for example, reduction of the corresponding oxime of structure 3: ##STR4## Suitable means for reducing the oximes of structure 3 include catalytic reductions employing hydrogen gas and a noble metal catalyst such as Raney nickel, platinum, palladium, rhodium, ruthenium or platinum oxide in an acidic alcoholic medium such as ethanol and hydrochloric acid; and dissolving metal reductions employing lithium, sodium, potassium, calcium, zinc, magnesium, or tin in liquid ammonia or a low-molecular weight aliphatic amine or sodium, aluminum or zinc amalgam, zinc, or tin in a hydroxylic solvent or in the presence of an aqueous mineral or organic acid such as formic acid, acetic acid, or hydrochloric acid.

The oximes of structure 3 can be prepared by any suitable art-known procedure such as nitrosation of the appropriate diketone of the structure 4: ##STR5## Suitable nitrosation reactions are reviewed by O. Tousler in "Organic Reactions" volume VII, pp. 327-377.

A slightly modified procedure is preferred when preparing the compounds of structure 1 wherein T is a divalent oxygen atom and R₂ is an optionally substituted pyridyl group. Essentially this procedure requires oxidation of the hydroxy group of the hydroxyimidazol-2-thione of structure 5: ##STR6## wherein R₁ is as defined in structure 1 and R₂ is an optionally substituted pyridyl group. This oxidation can be carried out in any convenient way using any suitable oxidizing agents. Suitable oxidizing agents for use in this process include manganese dioxide, aqueous acidic chromic acid in acetic acid or acetone; sodium dichromate in acetic acid; chromium trioxide-pyridine complexes such as the Sarrett or Collins reagents; potassium permanganate with aqueous sulfuric and acetic acids; 40% peracetic acid acid; m-chloroperbenzoic acid; tetrachlorobenzoquinine (DDQ); and N-haloimides preferably N-chlorosuccinimide.

Preferably the oxidation will be carried out using an N-haloimide such as 1,3-dibromo-5,5-dimethylhydantoin, 1,3-dichloro-5,5-dimethylhydantoin, N-chloroacetamide, N-bromosuccinimide or preferably N-chlorosuccinimide. These oxidations are performed by dissolving the compound of structure 5 in a suitable solvent to which 1 to 5 molar equivalents, preferably about 1 molar equivalent, of the N-haloimide is added. The reaction temperature can be from about 0° C. to about 80° C., preferably about room temperature, and will require from 1/2 hour to about 48 hours to be complete depending on the solvent, the temperature, and the oxidizing agent. Suitable solvents include any nonreactive solvent or mixture of solvents such as dimethylacetamide, methanol, dimethylformamide, or preferably dimethyl-formamide-methanol cosolvent. The resulting product of structure 1 can be isolated in any appropriate manner generally known to those skilled in the art such as by precipitation and subsequent recrystallization.

Alternatively, the oxidation can be performed using manganese dioxide. The hydroxyimidazol-2-thione of structure 5 is dissolved in any suitable solvent to which one or more equivalents, preferably 2 or 3 equivalents, of manganese dioxide is added and is allowed to react for 15 minutes to 10 hours, preferably about 1 or 2 hours, depending on the solvent and the temperature which can be from 0° C. to 150° C., preferably about 25° C. to 80° C. Suitable solvents include pentane, chloroform, methylene chloride, benzene, acetone, or preferably acetic acid. The product can be isolated from the reaction mixture by any procedure commonly employed by those in the art, for example, by filtration and solvent removal.

The hydroxyimidazol-2-thione of structure 5 is prepared by cyclization of the hydroxyaminoketone of structure 6: ##STR7## The cyclization of the hydroxyaminoketone is accomplished by reaction with a thiocyanate salt, preferably sodium or potassium thiocyanate. This reaction is performed by mixing about 1 molar equivalent of the aminodiketone with about 1 to about 5 molar equivalents, preferably about 1 molar equivalent of the thiocyanate salt in a suitable solvent. The reaction is acid catalyzed and the additional presence of a mild acid, for example, a dilute mineral acid such as dilute hydrochloric acid, sulfuric acid, or phosphoric acid, a carboxylic acid such as acetic acid, trifluoroacetic acid, benzoic acid, or formic acid, or a sulfonic acid such as methanesulfonic acid or p-toluenesulfonic acid in the reaction mixture is preferred. Preferably the solvent will act as the acid catalyst. The reaction is allowed to proceed for about 5 minutes to about 10 hours depending on, for example, the solvent and the temperature which can be from about 0° C. to about 100° C. Conveniently the reaction can be carried out at room temperature, i.e. about 25° C., and this is preferred. Suitable solvents for this reaction can be any non-reactive solvent such as water or a water miscible solvent, for example, an organic acid such as acetic acid; an alcohol such as methanol or ethanol; or an ether such as tetrahydrofuran or p-dioxan. Preferably any non-aqueous solvent will be mixed with water. The preferred solvent is a mixture of acetic acid and water.

The product of this reaction can be isolated by any suitable art known procedure such as by precipitation or by evaporation of the reaction solvent. The product can be successfully purified by recrystallization from a mixture of ethanol and methanol. Conveniently when the solvent is a mixture of acetic acid and water and potassium thiocyanate is the thiocyanate salt, the product separates from the reaction mixture as a crystalline substance which can then readily be isolated by filtration.

The hydroxyaminoketone of structure 6 is prepared by reduction of the corresponding diketooxime of structure 3. Preferred means for reducing the oxime of structure 3 wherein R₂ is an optionally substituted pyridyl group include catalytic reductions employing hydrogen gas and a noble metal catalyst such as Raney nickel, platinum, palladium, rhodium, ruthenium or platinum oxide; and dissolving metal reductions employing lithium, sodium, potassium, calcium, zinc, magnesium, or tin in liquid ammonia or a low-molecular weight aliphatic amine or sodium, aluminum or zinc amalgam, zinc, or tin in a hydroxylic solvent or in the presence of an aqueous mineral or organic acid such as formic acid, acetic acid, or hydrochloric acid.

The compounds of structure 1 wherein T is a divalent sulfur atom are prepared from the corresponding structure 1 compound wherein T is a divalent oxygen atom by reaction with phosphorus pentasulfide, P₂ S₅, using procedures generally known in the art. This reaction may be performed by mixing about 1 molar equivalent of the imidazol-2-thione of structure 1 wherein T is a divalent oxygen atom with about 1 to about 5, preferably about 1, molar equivalent of P₂ S₅ together with a suitable solvent. This reaction is allowed to proceed for about 1 to about 10 hours, preferably about 5 hours, depending on the reactants, the solvent, and the temperature which can be from about 25° C. to about 120° C., preferably about 50-80° C. Suitable solvents for this reaction can be any non-reactive solvent, for example, tetrahydrofuran (THF), p-dioxan, benzene, toluene, or pyridine. The preferred solvent is toluene.

The amount of the active ingredient to be administered can vary widely according to the particular dosage unit employed, the mode of administration, the period of treatment, the age and sex of the patient treated and the nature and extent of the disorder treated. The total amount of the active ingredient to be administered will generally range from about 1 mg/kg to 100 mg/kg and preferably from 3 mg/kg to 30 mg/kg. A unit dosage may contain from 25 to 525 mg of active ingredient, and can be taken one or more times per day. The active compound of formula 1 can be administered with a pharmaceutical carrier using conventional dosage unit forms either orally, parenterally, or topically.

For oral administration the compounds can be formulated into solid or liquid preparations such as capsules, pills, tablets, troches, lozenges, melts, powders, solutions, suspensions, or emulsions. The solid unit dosage forms can be a capsule which can be of the ordinary hard- or soft-shelled gelatin type containing, for example, surfactants, lubricants, and inert fillers such as lactose, sucrose, calcium phosphate, and cornstarch. In another embodiment the compounds of this invention can be tableted with conventional tablet bases such as lactose, sucrose, or cornstarch in combination with binders such as acacia, cornstarch, or gelatin, disintegrating agents intented to assist the break-up and dissolution of the tablet following administration such as potato starch, alginic acid, corn starch, or guar gum, lubricants intented to improve the flow of tablet granulations and to prevent the adhesion of tablet material to the surfaces of the tablet dies and punches, for example, talc, stearic acid, or magnesium, calcium, or zinc stearate, dyes, coloring agents, and flavoring agents intented to enhance the aesthetic qualities of the tablets and make them more acceptable to the patient. Suitable excipients for use in oral liquid dosage forms include diluents such as water and alcohols, for example, ethanol, benzyl alcohol, and the polyethylene alcohols, either with or without the addition of a pharmaceutically acceptably surfactant, suspending agent, or emulsifying agent.

The compounds of this invention may also be administered parenterally, that is, subcutaneously, intravenously, intramuscularly, or interperitoneally, as injectable dosages of the compound in a physiologically acceptable diluent with a pharmaceutical carrier which can be a sterile liquid or mixture of liquids such as water, saline, aqueous dextrose and related sugar solutions, an alcohol such as ethanol, isopropanol, or hexadecyl alcohol, glycols such as propylene glycol or polyethylene glycol, glycerol ketals such as 2,2-dimethyl-1,3-dioxolane-4-methanol, ethers such as poly(ethyleneglycol) 400, an oil, a fatty acid, a fatty acid ester or glyceride, or an acetylated fatty acid glyceride with or without the addition of a pharmaceutically acceptable surfactant such as a soap or a detergent, suspending agent such as pectin, carbomers, methylcellulose, hydroxypropylmethylcellulose, or carboxymethylcellulose, or emulsifying agent and other pharmaceutically adjuvants. Illustrative of oils which can be used in the parenteral formulations of this invention are those of petroleum, animal, vegetable, or synthetic origin, for example, peanut oil, soybean oil, sesame oil, cottonseed oil, corn oil, olive oil, petrolatum, and mineral oil. Suitable fatty acids include oleic acid, stearic acid, and isostearic acid. Suitable fatty acid esters are, for example, ethyl oleate and isopropyl myristate. Suitable soaps include fatty alkali metal, ammonium, and triethanolamine salts and suitable detergents include cationic detergents, for example, dimethyl dialkyl ammonium halides, alkyl pyridinium halides, and alkylamines acetates; anionic detergents, for example, alkyl, aryl, and olefin sulfonates, alkyl, olefin, ether, and monoglyceride sulfates, and sulfosuccinates; nonionic detergents, for example, fatty amine oxides, fatty acid alkanolamides, and polyoxyethylenepolypropylene copolymers; and amphoteric detergents, for example, alkyl-beta-aminopropionates, and 2-alkylimidazoline quarternary ammonium salts, as well as mixtures. The parenteral compositions of this invention will typically contain from about 0.5 to about 25% by weight of the active ingredient in solution. Preservatives and buffers may also be used advantageously. In order to minimize or eliminate irritation at the site of injection, such compositions may contain a non-ionic surfactant having a hydrophile-lipophile balance (HLB) of from about 12 to about 17. The quantity of surfactant in such formulations ranges from about 5 to about 15% by weight. The surfactant can be a single component having the above HLB or can be a mixture of two or more components having the desired HLB. Illustrative of surfactants used in parenteral formulations are the class of polyethylene sorbitan fatty acid esters, for example, sorbitan monooleate and the high molecular weight adducts of ethylene oxide with a hydrophobic base, formed by the condensation of propylene oxide with propylene glycol. A preferred mode of administration is by intraveneous injection or by an intracardiac catheter and will preferably employ an aqueous solution of a compound of structure 1 with sodium hydroxide, preferably about a 12N solution of sodium hydroxide.

The active ingredient may also be administered by means of a sustained release system whereby the compound of formula 1 is gradually released at a controlled, uniform rate form an inert or bioerodible carrier by means of diffusion, osmosis, or disintegration of the carrier during the treatment period. Controlled release drug delivery systems may be in the form of a patch or bandage applied to the skin or to the buccal, sublingual, or intranasal membranes, or a gradually eroding tablet or capsule or a gastrointestinal reservoir administered orally. Administration by means of such sustained release delivery systems permits the tissues of the body to be exposed constantly for a prolonged time period to a therapeutically or prophylactically effective dosage of a compound of formula 1. The unit dosage of the compound administered by means of a sustained release system will approximate the amount of an effective daily dosage multiplied by the maximum number of days during which the carrier is to remain on or in the body of the host. The sustained release carrier may be in the form of a solid or porous matrix or reservoir and may be formed from one or more natural or synthetic polymers, including modified or unmodified cellulose, starch, gelatin, collagen, rubber, polyolefins, polyamides, polyacrylates, polyalcohols, polyethers, polyesters, polyurethanes, polysulphones, polysiloxanes, and polyimides as wells as mixtures and copolymers of these polymers. The compounds of formula 1 may be incorporated in the sustained release carrier in a pure form or may be dissolved in any suitable liquid or solid vehicle, including the polymer of which the sustained release carrier is formed.

As used herein the term patient is taken to mean warm blooded animals, for example, birds such as chickens and turkeys, and mammals such as primates including humans, sheep, horses, cattle, pigs, cats, dogs, rats, and mice.

Reperfusion injury is that injury which occurs when molecular oxygen is reintroduced into an ischemic tissue. The ischemia can be caused by any means and in any tissue and includes ischemia to the heart or a portion of the heart resulting from a coronary thrombosis or any other blockage of the blood supply to the heart or a portion of the heart, ischemia surgically induced to the heart of a patient undergoing open-heart or coronary by-pass surgery, the ischemia which occurs to an organ or organ group such as a heart, heart-lung, liver, or kidney to be used in an organ transplant, ischemia occuring during circulatory shock, and ischemia which is caused by blockage of the arteries supplying the brain, i.e. stroke. The compound of structure 1 will ideally be administered to the patient at the time of tissue reperfusion and will continue until such time that reperfusion injury of the type being treated has normally ceased and will be for about 2 to 3 days following substantial reperfusion of the tissue. For example, the compound of structure 1 could conveniently be administered to a patient with a coronary thrombosis concurrently with the administration of a clot dissolving agent such as streptokinase or urokinase. Administration of a compound of structure 1 prior to an ischemia may be indicated in certain instances such as where a patient has substantial risk of heart attack or stroke and would continue until the risk of an ischemic event has substantially disappeared, for example, where the patient has recently suffered a heart attack or stroke, or where the patient is to undergo a surgical procedure requiring a temporary, surgically-induced organ ischemia such as in open heart surgery or coronary by-pass surgery. Use of the compounds of structure 1 to treat reperfusion injury to the heart is the use considered most significant. The ability of the compound of this invention to reduce reperfusion injury can be demonstrated by its ability to reduce myocardial stunning, i.e. the prolonged loss of contractile function in the absence of necrosis following short periods of myocardial ischemia. (See E. Braunwald and R. A. Kloner, Circ. 66, 1146-1149 (1982). Stunning has been implicated in a variety of disorders and conditions in which blood circulation has been temporarily cut off from the heart or in which a relatively high concentration of oxygen derived free radicals is known to be present.

In order to measure stunning an anesthetized dog is instrumented to record blood pressure, heart rate electrocardiogram (ECG), cardiac contractile force, and left intraventricular systolic pressure and its derivative. Two crystal sets each with two crystals are implanted in the left myocardium to measure shortening of the myocardial segments between the crystals of each set. One set is placed toward the base and the other toward the apex. The apical crystal set is placed to be within the ischemic area during occlusion of the left anterior descending coronary artery (LAD) at an intermediate point. The basal set of crystals are placed in the normal myocardium during ischemia. Following a control period, the LAD is occluded for 15 minutes followed by 3 hours of reperfusion. A short period of occlusion is used to prevent any substantial necrosis. During the period of occlusion, the shortening of the myocardial segment between the apical crystals ischemic myocardium) decreases and actually shows a lengthening during contraction in control dogs whereas the shortening between the basal crystals (nonischemic myocardium) is maintained. When the occlusion period is ended and reperfusion of the ischemic myocardium has commenced, contractility of the previously ischemic area improves but does not recover during the 3 hour reperfusion period. This disparity in contractility (reported as per cent shortening) between the normal and previously ischemic region is referred to as stunning and is reported below in Table 1 for the thio analog of enoximone, 1,3-dihydro-4-methyl-5-[4-(methylthio)benzoyl]imidazol-2-thione. To avoid any possible effect on stunning by the positive inotropic activity of the compound of this invention, the positive inotropic effect of the compound was allowed to dissipate at least 80 per cent prior to occlusion of the LAD.

                                      TABLE 1                                      __________________________________________________________________________     PREVENTION OF MYOCARDIAL STUNNING                                              DURING REPERFUSION FOLLOWING 15 MINUTES                                        OF ISCHEMIA IN ANESTHETIZED DOGS                                               (% Myocardial Fiber Shortening ± SE)                                                  BEFORE LAD                                                                     OCCLUSION     DURING LAD    DURING                                                    (PRE-) OCCLUSION     REPERFUSION                                        NORMAL ISCHEMIC                                                                              NORMAL ISCHEMIC                                                                              NORMAL ISCHEMIC                          TREATMENT                                                                              N AREA   AREA   AREA   AREA   AREA   AREA                              __________________________________________________________________________     Vehicle 7 12.4 ± 2.2                                                                         15.4 ± 1.3                                                                         14.4 ± 2.3                                                                         -3.2 ± 1.7.sup.a                                                                   13.8 ± 2.2                                                                         5.6 ± 1.7.sup.a,b              Thio Analog of                                                                         3 14.6 ± 2.3                                                                         17.2 ± 0.9                                                                         14.8 ± 3.7                                                                          2.8 ± 3.1.sup.a                                                                   13.9 ± 3.2                                                                         12.1 ± 2.2 .sup.               Enoximone                                                                      Milrinone                                                                              3 12.4 ± 0.2                                                                         16.4 ± 2.4                                                                         14.2 ± 1.6                                                                         -4.7 ± 4.3.sup.a                                                                   12.1 ± 1.4                                                                         3.7 ± 5.9.sup.a,b              __________________________________________________________________________      .sup.a Significant difference from percent shortening in the normal area.      .sup.a This disparity in shortening from the normal area indicates             stunning.                                                                

EXAMPLES

The following examples are intended to illustrate this invention and are not intended to limit the scope of this invention in any way.

EXAMPLE 1 Preparation of 1,3-dihydro-4-methyl-5-benzoyl-2H-imidazol-2-thione

Potassium thiocyanate (14.5 g, 0.15 mole) was added to a solution of 2-amino-1-phenyl-1,3-butadione (9.8 g, 0.055 mole) in 1N hydrochloric acid (200 ml.). The resulting solution was warmed on a steam bath for thirty minutes, then cooled. The crude product precipitated from the reaction mixture and was isolated by filtration. Subsequent recrystallization from ethanol gave pure title compound, m.p. 268°-269° C.

In a like manner, but substituting 2-amino-1-(2,3-methylenedioxyphenyl)-1,3-pentadione; 2-amino-4-methyl-1-[2-(1H-pyrryl)]-1,3-pentadione; or 2-amino-1-(3,4-methylenedioxyphenyl)-1,3-hexadione for 2-amino-1-phenyl-1,3-butadione in the above example, results in 1,3-dihydro-4-ethyl-5-(2,3-methylenedioxybenzoyl)-2H-imidazol-2-thione; 1,3-dihydro-4-isopropyl-5-[2-(lH-pyrrolyl]-2H-imidazol-2-thione; and 1,3-dihydro-4-propyl-5-(3,4-methylenedioxyphenyl)-2H-imidazol-2-thione, respectively.

EXAMPLE 2 Preparation of 1,3-dihydro-4-(4-methoxybenzoyl)-5-methyl-2H-imidazol-2-thione

Potassium thiocyanate (1.66 g, 0.017 mole) was added to a solution of 2-amino-1-(4-methoxyphenyl)-1,3-butadione (1.77 g, 0.0086 mole) in 1N hydrochloric acid (100 ml.). The solution was heated on a steam bath for thirty minutes, then cooled. The title compound precipitated and was collected by simple filtration, m.p. 200° C.

EXAMPLE 3 Preparation of 1,3-dihydro-4-methyl-5-(4-cyanobenzoyl)-2H-imidazol-2-thione

Potassium thiocyanate (14.5 g, 0.15 mole) was added to a solution of 2-amino-1-(4-cyanophenyl)-1,3-butadione in 1N hydrochloric acid 200 ml.). The resulting solution was heated on a steam bath for thirty minutes, then cooled. The solid title compound was isolated by filtration and recrystallized from ethanol.

EXAMPLE 4 Preparation of 1,3-dihydro-4-methyl-5-[4-(methylthio)benzoly]-2H-imidazol-2-thione

A solution of potassium cyanate (4.0 g, 0.04 mole) in water (10 ml.) was added to a solution of 1-4[-(methylthio)benzoyl]-2-amino-butane-1,3-dione (5.3 g, 0.02 mole) in acetic acid (40 ml.). The mixture was stirred overnight at room temperature during which time the product precipitated from the reaction mixture. The precipitate was collected by filtration and recrystallized from ethanol/methanol to give the title compound, m.p. 295° C.

EXAMPLE 5 Preparation of 1,3-dihydro-4-ethyl-5-(4-pyridinylcarbonyl)-2H-imidazol-2-thione

A solution of 1-(4-pyridinylcarbonyl)-1-hydroxy-2-amino-3-pentanone dihydrochloride (5.0 g, 0.018 mole) and potassium thiocyanate (3.6 g, 0.037 mole) in water (100 ml.) was heated on a steam bath for 30 minutes after which the solvent was removed by evaporation. The solid residue was collected and dried to give 1,3-dihydro-4-ethyl-5-(4-pyridinyl)hydroxymethyl-2H-imidazol-2-thione (2.8 g). The intermediate hydroxyimidazol-2-thione was dissolved in dimethylformamide (80 ml.) and N-chlorosuccinimide (1.6 g, 0.012 mole) was added. The solution was stirred at room temperature for 24 hours, then filtered, and the filtrate concentrated to dryness. The residue was dissolved in water, then treated with sodium bicarbonate to give a solution with pH=7. The solution was filtered, then concentrated to dryness. The resulting residue was chromatographed on silica gel to give the title compound, m.p. 275° C.

In the same way but using the appropriate hydroxyaminoketone of structure 6, 1,3-dihydro-4-isonicotinoyl-2H-imidazol-2-thione; 4-[3-(n-butylthio)isonicotinoyl]-1,3-dihydro-5-methyl-2H-imidazol-2-thione; 4-(2-bromoisonicotinoyl)-1,3-dihydro-5-ethyl-2H-imidazol-2-thione; 4-[2-(n-butyl)isonicotinoyl]-1,3-dihydro-5-isopropyl-2H-imidazol-2-thione; 1,3-dihydro-4-ethyl-5-(3-methylisonicotinoyl)-2H-imidazol-2-thione can be prepared.

EXAMPLE 6 Preparation of a Tablet Formulation

Tablets can be prepared each having the following composition.

    ______________________________________                                                                QUANTITY                                                INGREDIENT             (mg)                                                    ______________________________________                                         1,3-Dihydro-4-ethyl-5-(4-pyridinylcarbonyl)-                                                          100                                                     2H-imidazol-2-thione                                                           Cornstarch             15                                                      Lactose                33.5                                                    Magnesium Stearate     1.5                                                     ______________________________________                                    

EXAMPLE 7 Preparation of a Tablet Formulation

Tablets can be prepared each having the following composition.

    ______________________________________                                                                  QUANTITY                                              INGREDIENT               (mg)                                                  ______________________________________                                         1,3-Dihydro-4-methyl-5-[4-(methylthiobenzoyl)-                                                          100                                                   2H-imidazol-2-thione                                                           Cornstarch               15                                                    Lactose                  33.5                                                  Magnesium Stearate       1.5                                                   ______________________________________                                    

EXAMPLE 8 Preparation of a Capsule Formulation

Capsules can be prepared each having the following composition.

    ______________________________________                                                                  QUANTITY                                              INGREDIENT               (mg)                                                  ______________________________________                                         1,3-Dihydro-4-methyl-5-[4-(methylthio)benzoyl]-                                                         400                                                   2H-imidazol-2-thione                                                           Talc                     40                                                    Sodium Carboxymethylcellulose                                                                           40                                                    Starch                   120                                                   ______________________________________                                    

EXAMPLE 9 Preparation of a Parenteral Formulation

A parenteral formulation is prepared each unit dosage having the following composition.

    ______________________________________                                         INGREDIENT                QUANTITY                                             ______________________________________                                         1,3-Dihydro-4-methyl-5-[4-(methylthio)benzoyl]-                                                          1.0     g                                            2H-imidazol-2-thione                                                           Polyoxyethylene Sorbitan Monooleate                                                                      2.0     g                                            Sodium Chloride           0.128   g                                            Water for injection qs ad 20.0    ml                                           ______________________________________                                     

We claim:
 1. A method of lessening reperfusion injury in a patient suffering from ischemia which comprises administering to the patient a therapeutically effective amount of a compound of the structure: ##STR8## wherein T is a divalent oxygen or sulfur group;R₁ is a hydrogen or a (C₁ -C₄) alkyl group; and R₂ is a phenyl group of the structure: ##STR9## wherein R₃, R₄, R₅, and R₆ are each selected from a hydrogen, (C₁ -C₄)alkyl, (C₁ -C₄) alkoxy, (C₁ -C₄)alkylthio, (C₁ -C₄)-alkylsulfoxide, (C₁ -C₄)alkylsulfone, hydroxy, halogen, trifluoromethyl, --NR'R" wherein R' and R" are each selected from a hydrogen or (C₁ -C₄)alkyl group, pyrrolidino, piperidino, morpholino, piperazino, N--(C₁ -C₄)-alkylpiperazino, cyano, carboxy, carboxamido, C₁ -C₄)-alkoxycarbonyl, amidino, and 1-, 2-, 3-, 4-, or 5-imidazolyl, and any two adjacent R₃, R₄, R₅, and R₆ groups can taken together form a methylenedioxy group and with the proviso that when one of R₃, R₄, R₅, or R₆ is a --NR'R", pyrrolidino, piperidino, morpholino, piperazino, or N--(C₁ -C₄)alkylpiperazino group then at least two of R₃, R₄, R₅, and R.sub. 6 must be a hydrogen group; or R₂ is a pyridyl group optionally having one or two substituents selected from (C₁ -C₄)alkyl, (C₁ -C₄)alkoxy, (C₁ -C₄)alkylthio, (C₁ -C₄)alkylsulfoxide, (C₁ -C₄)alkylsulfone, trifluoromethyl, cyano, carboxy, carboxamido, amidino, and 1-, 2-, 3-, 4-, or 5-imidazolyl; or R₂ is a 2- or 3-(1H)-pyrryl, 2- or 3-thienyl, or 2- or 3-furanyl; ora pharmaceutically acceptable salt thereof.
 2. A method of claim 1 wherein T is a divalent oxygen group.
 3. A method of claim 1 or 2 wherein R₂ is an optionally substituted pyridyl group.
 4. A method of claim 1 or 2 wherein R₂ is an unsubstituted pyridyl group.
 5. A method of claim 3 wherein R₂ is a 4-pyridyl group.
 6. A method of claim 1 or 2 wherein R₂ is a phenyl group.
 7. A method of claim 6 wherein one of R₃, R₄, R₅, or R₆ is a (C₁ -C₄)alkylthio group or a 1-, 2-, 3-, 4-, or 5-imidazolyl group.
 8. A method of claim 6 wherein R₂ is a phenyl group and R₃, R₄, and R₆ are each a hydrogen group.
 9. A method of claim 6 wherein R₅ is a (C₁ -C₄) alkylthio group.
 10. A method of claim 6 wherein R₅ is a 1-, 2-, 3-, 4-, or 5-imidizoyl group.
 11. A method of claim 6 wherein R₅ is a methylthio group.
 12. A method of claim 1 wherein R₁ is a methyl group.
 13. A method of claim 1 wherein R₁ is an ethyl group.
 14. A method of claim 1 wherein the reperfusion injury is to the heart.
 15. A method of claim 4 wherein R₂ is a 4-pyridyl group.
 16. A method of claim 8 wherein R₅ is a (C₁ -C₄)-alkylthio group.
 17. A method of claim 8 wherein R₅ is a 1-, 2-, 3-, 4-, or 5-imidizoyl group.
 18. A method of claim 8 wherein R₅ is a methylthio group. 